BTA-1 is an uncharged derivative of thioflavin-T that has high a affinity for Ab fibrils and shows very good brain entry and clearance. The Kd of [3H]BTA-1 for binding to AD brain is very similar to the Kd for binding to synthetic Ab fibrils. BTA-1 does not appear to bind significantly to common neuroreceptors or transporter sites. BTA-1 exhibits high affinity for amyloid deposits (Ki = 11 nM for Ab(1-40)). It crosses the blood brain barrier and displays up to 50-fold higher affinity than ThT. It selectively stains cerebral plaques and cerebrovascular amyloid deposits in the brains of PS1/APP transgenic mice.